- Evaluating existing, but unused data
derived from overlay testers could be a key in creating
longer lasting pavements.
Researchers with the University of Texas at El Paso,
looked at mixed design characteristics.
In combination with that mixtures fatigue
cracking resistance numbers.
- TxDOT put all of their kinda eggs in one basket
if you will,
with the overlay testers 10 plus years ago.
Other states are using, you know, semicircular,
bending beam, these other tests, and on a national level,
at one point,
they compared all of them and really their standard
deviations and coefficient variation on all of these
tests were all very very high.
Overlay was a little bit better.
So, and it was developed in Texas.
So we naturally said,
that's the one we want to progress with.
- [Imad] The issue with this test was the variability.
You know what,
the way they run this test is you test how many cycles it
takes for the specimen to fully crack from bottom to top.
And the variability of the number of cycles that it took for
this to happen was a lot greater than 20%.
And this was always an issue that TxDOT that had.
But if you look at the load versus cycle,
you would see that this test behaves very, very well.
So we start describing that curve,
looking at an equation.
And from that equation, you come up with an index
and that index seemed to be very repeatable.
And not only that, it was repeatable,
we were also being able to delineate between the different
mixes.
The problem was when you get close to the margin
as Mike says, you know,
it's very difficult to interpret.
If one test you run three times and one says that it's good.
The other one says it's bad.
And the third one, it says good or bad, doesn't matter.
So you don't have a good feeling.
Now we consistently get three results that all three of them
are bad, or all three of them are good, even at the margin.
So there's more confidence in the results that you get from
the system, because there is also more repeatable.
- This is a national thing that everybody's looking at a
balanced mix design process,
and everybody has the same thought that you have to balance
cracking and you have to balance rutting.
To my knowledge at this point, with the new analysis,
this has the lowest coefficient of variation.
So this is now a reliable cracking test.
It gives you a much higher level of confidence on that
cracking side. And so I think to balance them,
you have to have both cracking and rutting so that we can
move forward with this balanced mixes on.
- For more information,
and to find the publications for this project,
please visit the TxDOT research library
at the link shown below.